Technology for die cast molding a metal melt such as an aluminum alloy is currently widely used, and recently, die casting methods using slurry-form semi-solid metal in which solid and liquid are both present together, regarded as suited to increasing mold life and increasing the dimensional accuracy of die cast moldings, have been receiving attention.
In a die casting method using a semi-solid metal, management of solid phase percentage, which expresses the ratio of solid to liquid in the molten alloy, is important. In inventions pertaining to this solid phase percentage management, for example a method wherein a target solid phase percentage is sought to be obtained by temperature management up to the transformation point of the semi-solid metal and then for a fixed time from the transformation point performing time management of stirring and cooling is known in JP-A-2002-153945.
FIG. 35 shows with a flow chart a method for obtaining a target solid phase percentage set forth in JP-A-2002-153945.
First, a control start time Ts is inputted. Then, stirring and cooling of a semi-solid metal in a vessel is started, and a semi-solid metal temperature measured with a thermocouple is read in.
Here, the elapsed time from the start of cooling is written Time, and until this elapsed time Time reaches a time Ts, stirring and cooling are continued and reading in of the semi-solid metal temperature is continued. When the elapsed time Time reaches the time Ts, the process moves on to a next step ST05.
ST05 estimates a transition point Pt from a cooling curve. ST06 obtains a cooling time Tf corresponding to the transition point Pt, i.e. a cooling time to a target solid phase percentage being reached from the transition point Pt. ST07 ends the stirring and cooling when the cooling time after the transition point Pt has reached Tf, and then die casting is promptly started.
FIG. 36 shows the method for obtaining a target solid phase percentage set forth in JP-A-2002-153945 with a graph, and supplements ST07 of FIG. 35. It assumes that the target solid phase percentage can be reached by stirring for the cooling time Tf from the transition point Pt of the semi-solid metal.
In this JP-A-2002-153945, it is taken as a premise that the cooling rate does not change around the transition point.
However, generally the properties of a metal change around its transition point, and inevitably a difference arises between the cooling rate before the transition point and the cooling rate after the transition point.
This difference appears as a difference between the target solid phase percentage and the actual solid phase percentage, and as a result the solid phase percentage management accuracy falls.
In recent years, along with a demand for higher-level casting technology, it has become necessary to raise solid phase percentage management accuracy of semi-solid metals. So, management technology to replace the time-based solid phase percentage management of related art is awaited.
In related art, as a production line of a metal molding made by die cast molding of this kind, one having a vessel capable of receiving a predetermined amount of melt, a semi-solid metal production apparatus for making a semi-solid metal by stirring and cooling melt in the vessel, a molding machine for molding a metal molded product with semi-solid metal as a starting material, a carrying apparatus consisting of a multiple joint robot for carrying the vessel from the semi-solid metal production apparatus to the molding machine and feeding the semi-solid metal in the vessel into the molding machine, and a vessel restoring apparatus for carrying out a predetermined restoring treatment on the vessel having been emptied by the pouring of the semi-solid metal into the molding machine, is known for example in JP-A-2001-170765.
In this technology, the vessel restoring apparatus has air blowing means for removing metal adhered to the inside of the vessel while cooling the vessel by blowing air at the inside of the vessel, and coating means for applying releasing agent to the inside of the vessel.
A line in which in addition to air blowing means and coating means, brushing means for cleaning the inside of the vessel with a brush after the treatment with the air blowing means is added to the vessel restoring apparatus is known, for example in JP-A-2002-336946.
The air blowing means of these vessel restoring apparatuses of related art act so as to solidify semi-solid metal remaining adhered to the inner face of the vessel into a granular form and blow it off, but when semi-solid metal remains in relatively large lumps, it is difficult to solidify and blow these off. When semi-solid metal has remained and solidified in large lumps, it is not possible to remove these by brushing means either, and the frequency of adhered metal remaining in the vessel becomes high. Because of this, in related art, the presence or absence of adhered metal in the vessel is checked visually after the restoring treatment of the vessel restoring apparatus, and when adhered metal remains, the vessel is removed to outside the line and work to remove the adhered metal is carried out. As a result, it becomes necessary to anticipate restoring work outside the line and prepare a larger number of vessels, and this leads to an increase in initial cost.
And, for the production of semi-solid metal, temperature management of the vessel is important, and it is necessary for the vessel to be cooled to a predetermined temperature with air blowing means. However, when semi-solid metal remains inside the vessel in relatively large lumps, the vessel does not readily cool, the cooling of the vessel takes time, and this constitutes a problem in achieving productivity increases.
Thus, a metal molded product manufacturing line on which even if semi-solid metal remains in a vessel in relatively large lumps this can be efficiently removed and the problems described above are resolved has been awaited.
Also, as a production line of a metal molded product of related art, one having a semi-solid metal production apparatus for making a semi-solid metal by cooling and stirring a melt received in a vessel with a stirring head having a cooling metal that is immersed in the melt, wherein the vessel is carried from the semi-solid metal production apparatus to a molding machine and semi-solid metal in the vessel is fed into the molding machine, is known.
Here, when semi-solid metal adheres to a cooling metal of the stirring head and the next production of semi-solid metal is carried out with it still left there, solid matter having adhered to the cooling metal and solidified detaches in the vessel and quality deterioration of the semi-solid metal occurs, and plant trouble of solidified matter interfering with the vessel and so on arises. To avoid this, in related art, a line in which a stirring head restoring apparatus is disposed adjacent to the semi-solid metal production apparatus and carries out a predetermined restoring treatment on the stirring head after the production of the semi-solid metal is known, for example in JP-A-2002-336946. This stirring head restoring apparatus has cooling means for cooling the cooling metal of the stirring head by dipping it in water and coating means for applying a releasing agent to the cooling metal. When the cooling metal is dipped in water by the cooling means, the water flash-boils, and the energy of the flash-boiling causes adhered metal to detach and fall from the cooling metal.
One has been proposed in which in addition to the cooling metal a probe for measuring viscosity is attached to the stirring head, and the probe is immersed in the melt in the vessel together with the cooling metal and production of the semi-solid metal is carried out so that the viscosity value measured by the probe reaches a target value.
When a probe is attached to the stirring head like this, semi-solid metal adheres to the probe also. It was thought that when the probe was dipped in water together with the cooling metal by the cooling means of the stirring head restoring apparatus described above, adhered metal would detach and fall from the probe under the energy of flash-boiling of the water; however, in practice, because compared to a cooling metal the heat capacity of a probe is extremely small, the energy of the flash-boiling around the probe is not strong enough for the adhered metal to detach and fall, and the adhered metal tended to remain on the probe. And, the probe remains immersed in the water until the cooling metal has been cooled to the optimal temperature, and with this the problem also arises that the temperature of the probe, which has a small heat capacity, falls too far, and it is difficult for the releasing agent applied to dry in the subsequent coating step.
So, a stirring head restoring apparatus and restoring method of a semi-solid metal production apparatus have been awaited with which, in the restoring treatment of a stirring head fitted with a probe, metal adhered to the probe can be removed efficiently and excessive cooling of the probe can also be prevented.
Also, in related art, slurry-form semi-solid metal injection-molding technology is known, for example in JP-A-2002-336946.
Technology set forth in JP-A-2002-336946 will now be explained on the basis of the next figure.
FIG. 37 shows technology set forth in JP-A-2002-336946. The S1 to S11 below denote a step 1 to a step 11.
First, in S1, 1 shot of melt is received into a ladle from a melt holding furnace.
Then, in S2, the ladle is carried to a stirring station, and there is transferred to a first vessel.
In S3, the melt in the first vessel is stirred at the stirring station, brought to a state wherein both solid and liquid are present, and brought to a desired solid phase percentage. The temperature at this time is uniform.
Next, in S4 the first vessel is carried to an injection-molding machine.
Meanwhile, in S5, closing of a mold is carried out in parallel at the injection-molding machine.
Then, in S6, melt is poured from the first vessel into an injection sleeve, and in S7 injection into the mold is carried out.
In S8 air is blown at the emptied first vessel, in S9 the inside of the first vessel is cleaned by a brushing treatment, and in S10 coating of the inside of the first vessel is carried out.
In S11, if the number of moldings manufactured has reached a predetermined number, production is ended. If it has not, the process returns to S1 and production continues.
Now, because the semi-solid metal is a mixture of solid phase and liquid phase, management of its solid phase percentage (=solid phase/(liquid phase+solid phase) %) is important. This is because if the solid phase percentage differs, the quality of the molding obtained changes.
In S3 of FIG. 37, the melt in the first vessel is stirred with a cooling metal and, due to a heat-removing action that accompanies this stirring, cooling proceeds and the viscosity of the melt rises and its solid phase percentage rises.
Therefore, in the management of the solid phase percentage, the stirring of the melt becomes important.
However, in the related art technology mentioned above, when manufacturing was carried out to obtain multiple moldings with a fixed solid phase percentage, the stirring time required varied greatly.
When the stirring time is extremely long, because the time for which the injection-molding machine is kept waiting becomes too long, productivity falls. When the stirring time is extremely short, because the injection-molding machine becomes unable to keep up, it is necessary to limit the number of vessels circulated, and productivity falls.
That is, to circulate multiple vessels optimally and operate the injection-molding machine well, it is necessary to minimize variations in stirring time.
So, technology has been awaited with which, in semi-solid metal injection-molding, it is possible to suppress variations in the duration of stirring carried out to keep the solid phase percentage of the melt constant.
Products manufactured using die casting include for example a cylinder block of an engine. A water jacket serving as a cooling water passage is provided in this cylinder block, and there are an open deck type, in which the water jacket opens at the cylinder head face; a closed deck type, in which the water jacket is closed; and a semi-closed deck type, in which part of the water jacket is open at the cylinder head face. Because at the cylinder head face the cylinder bores and the cylinder outer wall parts are connected, cylinder blocks of the closed deck type and the semi-closed deck type are highly rigid, suffer little deformation, and moreover have long life. Because in these closed deck type and semi-closed deck type cylinder blocks the water jacket is of a closed shape, at the time of casting it is not possible to use a durable trimming die for the water jacket, and a breakable core that can be crumbled and removed after casting, for example a sand core, is used.
On the other hand, the cylinder block is a main constituent part of the engine, and because heat and pressure act upon it it is also an important part strengthwise. Therefore, when a cylinder block is cast, it is desirable that the occurrence of nesting be suppressed. As one means for preventing nesting, there is the example of using a slurry-form semi-solid metal as the casting material. A semi-solid metal is a metal in a state such that solid and liquid are present together, and because its viscosity is high there is little entrainment of gas and the occurrence of nesting can be kept down.
As related existing technology, in JP-B55-19704, a die casting method is set forth wherein the occurrence of surge is suppressed by the piston being stopped just before the melt is completely injected into a cavity having a sand core.
In JP-A-9-57415, a method is set forth wherein the speed of the melt at a weir at the time of melt injection is made a low speed of ⅕ to 1/50 of that in an ordinary die casting method.
In JP-A-11-104802, a die casting method is set forth wherein a slurry-form semi-solid metal is prevented from penetrating a core by the average particle size of its solid phase part being adjusted.
Now, a slurry-form semi-solid metal has intermediate properties between a liquid and a solid, and compared to a liquid its viscosity is high. Consequently, if a semi-solid metal is made to impact a sand core at a high speed, there is a risk of the sand core breaking. In particular, a thin sand core for forming something like a water jacket will readily break when hit by a highly viscous semi-solid metal and yield of the product will fall. Because a sand core must be removed after casting, it is desirable that it crumble easily, and it cannot be made too hard.
To prevent breakage of a sand core during casting it is conceivable to lower the speed at which the semi-solid metal is poured, but when pouring takes a long time the semi-solid metal hardens, or as a result of its temperature falling its solid phase percentage changes, and there is a risk of the required run ability not being obtained. As a result of the temperature falling the viscosity of the semi-solid metal becomes still higher, and again there is a risk of breaking the sand core.
In the method set forth in the above-mentioned JP-B-55-19704, although the piston is stopped just before the melt has filled the volume inside a cavity having a sand core and surging is thereby suppressed, when it hits the sand core the melt is at a high speed. If it were an ordinary melt, even when impacted at a high speed the sand core would not break; but when a semi-solid metal hits it at high speed there is a risk of it breaking, as mentioned above. And when as in JP-A-9-57415 the pouring speed is made extremely low, the pouring time becomes long, and although with an ordinary melt there is no problem, with a semi-solid metal there is the concern that it will harden or its run ability will fall.
So, a die casting method has been awaited with which the occurrence of nesting is suppressed by a semi-solid metal being used as the casting material and there is no breaking of sand cores and the yield of the cast moldings can be increased.